Down Feather insulated sleeping bags are very commonly found in the marketplace today. Although different products from different brands may give different looks to the product, the basic construction technique remains for more than 20 years. The basic idea behind any down construction technique is to create a compartment of space, to fill it with down content and to close the fill hole.
Down, as an insulation material, behaves like a fluid in which it will shift to area with lower density. So the key in designing a down sleeping bag is to attain a fine balance between filling weight (amount of down) and the volume of space. Because of this limitation, most of the products we find in the marketplace, although with different colors and aesthetic, basically share the same common construction atomony. Below are the two commonly used down construction techniques:                Sewn-Through Construction (FIG. 1)—This is a very simple form of construction which is very commonly found in lighter weight/lower end product. The basic construction is very simple: stitching together two pieces of fabrics together creates compartment “tunnel”, which one will fill the “tunnel” with down feather content. The drawback with this construction is that there is no down coverage along each stitch line (generally call “cold spots”), and thus giving an uneven thermal performance. As a result, this construction technique is only found in lighter weight/lower end product where thermal performance is not very critical.        Baffle Construction (FIG. 2)—This construction is widely used in most down product today. The idea is very similar to Sewn-Through construction and the only difference is the addition of a partition material called “baffle mesh”. The baffle mesh sits between the two fabrics and provides a “height” factor to the down compartment. As a result, the cold spots are eliminated in the process and thus offering a more even thermal experience to the user.        
The idea behind the above two constructions is to create a “hollow tube” for which the down will fill up the volume inside. The challenge is the bigger the volume, the more free space available and thus the higher chance of down shifting. Down shifting basically refers to the fact that the down over-shift from one side to the other, creating an imbalance coverage and thus affecting a consistent thermal performance. In order to avoid down shifting, it is important to limit the size/volume of each baffle compartment which results in very common finding in almost all down sleeping bag in the market today: horizontal baffling. Regardless of sizes, weight, constructions, brands, essentially all down sleeping bags are with horizontal baffling (FIG. 3).